1. Field of the Invention
This invention relates in general to facsimile transmitting and receiving devices particularly of the type that transmit such facsimiles over a telephone network.
2. Description of the Prior Art
Facsimile transmitting and receiving devices are in use for transmitting the contents of a document to a remote location, typically over telephone networks. In general, the devices have a rotatably driven drum. The document to be transmitted is secured around the drum. A scanning element is moved linearly across the document as the drum rotates. The scanning element detects differences in light intensity due to variations in the reflectivity of the scanned document. A photoelectric device in the scanning element converts the variations in light intensity into electric signals. The electric signals are transmitted to a receiving unit, which simultaneously converts the signals into images, producing a facsimile of the original document.
The receiving unit, which may be identical to the transmitting unit, has a rotatably driven drum that receives a sheet of copy medium, such as specially prepared paper. A printing head moves linearly across the drum as the drum rotates, and simultaneously creates an impression on the copy medium as the scanning head detects and transmits.
One problem concerns aligning the right and left hand margins on the copy medium with the margins on the original document. The scanning element of the transmitter has to be in alignment with the edge of the margin at the same time that the printing element of the receiving unit is in alignment with the edge of the margin. Otherwise, the material in the facsimile will be off-centered.
In U.S. Pat. Nos. 3,872,239 and 3,975,590, proposals are shown to eliminate the need for aligning the margins. Basically, a copy medium sheet is employed that has adhesive strips on its side. The sheet is folded over the drum and secured into a closed loop with the adhesive. The printing instrument may begin at any point. Once the facsimile has been completed, the loop of the copy medium is cut at an appropriate margin.
One disadvantage of this system is that the adhesive overlap may likely be in the middle or at any point in the sheet after removal. This may be objectionable for some uses. Also, specially prepared adhesive copy material is required.
Another disadvantageous feature in the prior art concerns the printing instrument. The type in general use has a high voltage unit that burns the copy medium at a given point when it receives a signal. This requires specially prepared copy medium, and is not workable with ordinary bond paper. Also, since the system requires high voltage and heat, it is expensive and may be more prone to failure than if these elements were not required. Printers that employ solenoid actuated hammers to strike a ribbon to transfer an image by pressure have been used for various purposes in the past. However, to applicant's knowledge, they have been used only with a flat sheet or with a drum that is stationary at the time of contact, not with a rotating drum. None have been used with facsimile transmitting devices, to applicant's knowledge.